Fig 1.
Geographical, topographic and geological overview of the study area.
The position is given within (A) Central Europe, (B) the Thuringian Basin, (C) within the wide valley now partially occupied by the river Gera and (D) at the SW footslope of the hill “Roter Berg”. Topographic information in panels A and B obtained using open-access SRTM data with a 90-m resolution (www.earthdata.nasa.gov/sensors/srtm). For panels C and D, a LiDAR Digital Elevation Model DEM1 with 1-m resolution was used, kindly provided by the Thuringian State Office for Land Management and Geoinformation (©GDI-Th, License: dl-de/by-2-0, https://geoportal.thueringen.de/gdi-th/download-offene-geodaten). Geological information, according to the German Stratigraphic Commission taken from the Digital Geological Map GK25; pedological information taken from the soil map BGK 100. Both were kindly provided by the Thuringian State Office for the Environment, Mining and Nature Conservation (© GDI-Th, License: dl-de/by-2-0, https://tlubn.thueringen.de/kartendienst). *The rough area of former wetlands was deduced from older topographic and geological maps from 1839 and 1931, respectively (see Supplementary Section 1 in Supplementary Information in S1 File).
Fig 2.
Graphical representations of the immediate study site. Panel A – Terrain levelling for the construction of the airfield in 1926 with the hill “Roter Berg” in the background (courtesy of Thuringian State Department for the Preservation of Monuments and Archeology TLDA; photo credits: Wilhelm Lorenz 1926). Panel B – Map of the excavation findings 1926/27 (Bolle, 1937). For location, the map includes a scale (lower right = “Maßstab”) and the directional distances to the nearest roads.
Abbreviations: FM = cemetery wall, M2 = second wall, Mgr. = mass grave, Egr. = individual graves (schematic), B = debris of the former church (schematic). Additional terms: “Scherben” = pottery sherds found at the northern edge of the excavation, “alter Fußweg” = former footpath, “180-m-Höhenlinie” = 180 m contour line, “190m bis Stott. Straße” = distance to the road ‘Stotternheimer Straße’. “Am Schwengelborn” refers to a toponym translating to ‘well sweep’. Panel C – Digital elevation model of the study area that displays all coring positions and the trace of all ERT-profiles included in the study (P2-P4, P6, P7, P11, P12). Also indicated in orange is the tentative position of notable features from the excavation in 1926/27 according to our preferential georeferenced version of the sketch by Bolle (1937), cf. Supplementary Section 2 in Supplementary Information in S1 File. Current land use marked by white text boxes. DEM provided by the Thuringian State Office for Land Management and Geoinformation (© GDI-Th, License: dl-de/by-2-0, https://geoportal.thueringen.de/gdi-th/download-offene-geodaten).
Table 1.
Characterization and interpretation of the Stratigraphic Units (SU) documented in the study area.
Fig 3.
Photographic documentation of representative coring sequences.
Cores EN-RK 7 and 58 refer to the Chernozem zone standard sequence; the Black Floodplain Soil (BFS) zone standard sequence is represented by core EN-RK 41. The attribution of the different deposits to stratigraphic units (SU) is indicated. Descriptions of SU1 to SU7 can be found in Table 1 and Supplementary Section 3 in Supplementary Information in S1 File. Cores EN-RK 55 and 56 were obtained in the position of the potential mass grave. SU1 and SU2 refer to the natural Keuper mudstone and the Lower Terrace fluvial gravels, respectively. The potential backfill deposits comprise the entire sequence above the upper boundary of SU2. Blue boxes indicate the main occurrence of well-preserved skeletal remains. Note that the brownish, gravelly material at the base of RK 55 (marked with a red X) represents contamination during core extraction.
Fig 4.
Simplified pedo- and lithostratigraphic sequences along the three coring transects T1 to T3.
The boundary between the Chernozem and the Black Floodplain Soil zone is depicted. The estimates for truncation/soil removal in the central parts of the transects caused by ground modification during the airfield construction in 1926/27 are indicated by the pale pink rectangles. Yellow bars specify the segments covered by the respective ERT profiles.
Fig 5.
ERT-profiles P2 to P4, P6 and P7.
The profiles P2 to P4 are aligned with the central sections of the coring transects T1 to T3; the models are based on the inversion of the Wenner configuration. Profiles P6 and P7 cross the potential mass grave in W-E and N-S directions, respectively. The models are based on a joint inversion of a Wenner and Dipole-Dipole configuration. The vertical and horizontal extent of the potential mass grave, as interpreted from consistent results of ERT and Pürckhauer mapping, is marked with black dashed lines.
Table 2.
Compilation and sampling context of different chronological information from the study area.
Fig 6.
Documentation of human bones and their radiocarbon dates.
A1 – Fragments of a longbone from EN-RK 55 (264 cm depth, TLDA Inv.No. 22/220-12), A2 – Fragments of cranial bones from EN-RK 55 (260 cm depth, TLDA Inv.No. 22/220-13), A3 – Bone fragments from EN-RK 56 (180 cm depth, TLDA Inv.No. 22/220-20). B – Numerical dates and calibration graphs for samples TLDA Inv.No. 22/220-13 and 22/220-20, which were subjected to radiocarbon dating. Calibration was done using OXCal v.4.4.2 and the IntCal20 curve (Reimer et al, 2020).
Fig 7.
Synoptic illustration of the main results.
ERT and coring results are integrated to infer the regionalization of the pedogeographic zones, with their boundary indicated as a white dashed line. Coring positions with presumed archeological subsurface features are marked in blue, positions with available chronological information are marked in red. Findings of previous archeological investigations are presented, as is the presumed position of the former cemetery wall (Supplementary Section 5.2 in Supplementary Information in S1 File) and extent of the potential mass grave, discovered in this study. *For details regarding the chronologies, see Table 2.